Leaving aside the absurd notion that most casualties in space battles = death, most of the battles shown, doesn't mean most of the battles that happened. When the Jem'Hadar are attacking and occupying entire worlds like Betazed, that's where most of your casualties are going to come from. So a series of AR-558, the Ship and Nor the Battle to the Strong scenarios. And casualties in those battles did not instantly equal death.
Normal, prolonged exposure heals your wounds and makes you immortal. The whole point of the collector was to collect the radiation particles for concentrated use. So I'm inclined to think they'd be more effective than the natural stuff and the only reason people wouldn't be immortal is because they aren't permanently exposed to the stuff.